1. Field of the Invention
The invention relates to electrometallurgy, and more particularly to methods and apparatus for smelting charge materials in electric arc furnaces.
The invention can find application in iron and steel production, nonferrous metallurgy, the chemical industry and the manufacture of refractories.
2. Description of the Prior Art
There is known a method for smelting charge (see F. P. Edneral "Elektrometallurgiya stali i ferrosplavov" /Electrometallurgy of steel and ferroalloys/, "Metallurgiya" Publishers, Moscow, 1977, pp. 103-157, pp. 378-454) in an ore-smelting or arc steelmaking furnace supplied with industrial frequency (f=50 Hz) alternating current, comprising loading a charge, melting it, conducting redox reactions and tapping a finished melt. Also known is an electric furnace plant for putting the above method into effect (L. E. Nikol'skii et al. "Promyshlennye ustanovki elektrodugovogo nagreva i ikh parametry" /Industrial plants for electric arc heating and their parameters/, "Energiya" Publishers, Moscow, 1971, pp. 16-26, pp. 94-109), which consists of a transformer coupled by the power supply arrangements with electrodes inserted into a bath of the electric arc furnace, mechanisms for positioning and slipping electrodes, and systems for automatically feeding the charge materials and adjusting the electric power input.
However, the above method involves excessive losses of energy as it provides no means for continuously adjusting the voltage and the position of the electrodes. The apparatus has a low natural power factor due to large reactance losses, with the reactive power amounting to 50-60% of the total power. The greater the energy losses are, the larger the electric furnace power rating is. The compensation of the reactive power necessitates additional equipment. In addition, the apparatus above suffers from high losses of active energy in the power supply arrangements because of the skin and the proximity effects, thus requiring much copper for conductors.
During smelting, it is necessary to re-position the electrodes of the electric arc furnace continually so as to adjust the power input thereto, this disturbing the thermal equilibrium in the bath of the electric arc furnace.
The above apparatus has large inherent electromagnetic losses in component metallic structures, the mechanical resistance of structural elements from magnetic materials dropping because they overheat.
Another disadvantage is a transfer of power between the phases, which causes irregularities in the distribution of energy in the electric arc furnace and results in lower both throughput capacity of the furnace and durability of refractory lining of the furnace. Due to the skin effect, the cross section of the supply conductors is utilized inefficiently, thus requiring greater both mass and dimensions of the power supply arrangements.
Yet another method for smelting a charge in a 21,000-kVA electric arc furnace (see "Spravochnik po elektrotermicheskomu oborudovaniyu" /Electrothermal equipment handbook/, "Energiya" Publishers, Moscow, 1971, Chapter 9) consists in a continuous loading of the charge (coke, quartzite and iron chips) into a bath of the electric arc furnace supplied with industrial-frequency alternating current. In the bath of the electric arc furnace, the thermal energy is released in the form of the Joule heat by the alternating current flowing through the charge and of heat radiated by the submerged arcing of the electrodes. The continuously evolving thermal energy heats the charge and melts it near the bottom of the bath. Melting proceeds along with the endothermal reduction of iron and silicon oxides by coke carbon which oxidizes to a gas and is removed from the electric arc furnace in the form of carbon monoxide and dioxide.
The reduced silicon dissolves in molten reduce iron, and a final melt trickles into the bath, wherefrom it is tapped into a ladle in the form of a ferrosilicon alloy and a small amount of slag.
An apparatus for putting this method for smelting charge materials in an electric arc furnace (see "Spravochnik po elektrotermicheskomu oborudovaniyu" /Electrothermal equipment handbook/, 1971, Chapter 9) into effect comprises a transformer connected by a secondary winding thereof through power supply arrangements to electrodes of the electric arc furnace, inserted in a bath of the electric arc furnace. The power supply arrangements are coupled with a unit for controlling the power input to the electric arc furnace by means of an electrode positioning mechanism coupled with the output of the unit for controlling the power input to the electric arc furnace.
Inherent in the above apparatus are excessive heat-losses caused by cooling water supplied inside chambers of structural elements from magnetic materials and by a large electromagnetic field permeating the space occupied by the furnace. These may amount to as much as 6-7% of the active power of the furnace. The high current intensity as compared to the voltage and the considerable reactance of the furnace circuit make it impossible to obtain an average monthly power factor above 0.80-0.82, this involving a high specific electric power consumption.
The copper power supply arrangements have a large cross section--21,600 mm.sup.2 --because of the inefficient utilization thereof.
It proves impossible to adjust smoothly the working voltage during smelting according to the above method because both the characteristics of the transformer and the electric service conditions of the apparatus are inappropriate with the effect that the electrodes have to be moved through as much as 1000 mm due to fluctuations in the electric resistance of the bath and the large voltage values of the transformer taps.